Sound is a physical vibration of particles. While we typically experience sound through the vibration of air, sound can also be heard through other materials, such as water and metal. Specifically, sound is a longitudinal wave, meaning that the virations of the particles move in the direction of the sound and not transverse (or perpendicular) to it. This is sometimes a bit confusing because many of the portrayals of sound give the impression that the sound is moving to the side while the wave form is up and down. The reason for this inaccuracy is that it’s simply much easier to display the magnitude of a vibration this way.

A more accurate demonstration of a longtiduinal wave is to stretch out a spring (or a slinky) and to shake it in the direction of the spring. You basically "push" the wave down the spring instead of "shaking" it. For this reason, sound is seen as a pressure wave as it is a literal change of pressure caused by the vibration of the molecules.

The pushing and pulling model accurately describes how speakers work. A speaker basically consists of a cone that is attached to an electromagnet that pushes the cone forward and backwards. Those forward and backward motions create the pressure wave that generates the sounds that we hear.

The experience of sound is a complex process. Typically, the sound vibrations hit our ear drums, causing the ear drum to vibrate. That vibration gets amplified in the middle ear (which is a collection of small bones), and those vibrations enter the innear ear and cochlea. The cochlea is a shell-shaped fluid-filled organ with nerves, and the stimulation of those nerves by the fluid creates the electrical signals that reaches our brain that leads to the experience of sound.

It is important to note that there are other ways to stimulate the inner ear without starting at the ear drum. There is another process known as bone conduction, which uses a device to vibrate the skull in a way that causes the same types of cochelar vibrations directly. This is a gimmick that is used in some magic tricks to give people audible instructions without creating noises that the audience can hear.